The alveoli and distal airways of the lungs are lined with an extracellular layer of material which is absolutely essential for the maintenance of normal pulmonary functions such as gas exchange. The most important component of the extracellular lining is a substance called pulmonary surfactant which serves to prevent collapse of the alveoli and distral airways at low lung volumes. Pulmonary surfactant is a complex-mixture of lipids and proteins whose nature and orgins form the basis of this research. The objectives of this study are 1) to identify the contribution of each lipid component to the overall function of pulmonary surfactant, 2) to elucidate the role of protein constituents in pulmonary surfactant, 3) to establish the role of complex lipid/protein structures as intermediates in the transformation of secreted lamellar bodies into pulmonary surfactant and 4) to clarify the relationship between the pulmonary surfactant system and the lysosomal enzyme system within the alveolar Type II cell.